I have something like that. It showed up on the slide of my 2018 Keystone Passport 2670BH last year. No sign of oil leak from the slide motor. Dealership looked at it and recommended we just keep an eye on it for now. I will be checking it again when I get the trailer out of winter storage in about about 3 weeks.
To me it looks like the top seal wiper has wiggled some of the TPO membrane loose from vibration while driving down the road. The line you can see along there is where the wiper part of the seal sits while the slide is closed.
https://www.keystoneforums.com/forum...ad.php?t=39053
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Stephen and Yolaine
2018 F-150 King Ranch SCrew (3.5 EB, Max Tow)
2018 Passport GT 2670BH (Using Equalizer 4 Pt)
Nova Scotia, Canada
Linear Mode
